Manufacture of partially acetylated paper



United States This invention relates to the treatment of paper prepared from partially acetylated cellulose fibers with a water emulsion containing a cellulose derivative and a plasticizer whereby the paper sheet is improved in wet strength, fold characteristics and Mullen value.

A simplified flow diagram of the method is as follows:

Paper prepared from partially acetylated cellulose fiber Wet and impregnated with an emulsion composed of cellulose ester or ethyl cellulose, plasticizer, Water and surfactant Run through hot calender rolls which redry the paper, fuse the cellulose compound-plasticizer mixture and bond the fibers Paper is ordinarily as wood pulp by applying a slurry of the fibers to the wire of a paper machine from which the thus formed paper is led eventually to calender rolls to impart a smooth, even finish thereto. To improve the characteristics of such paper, sizing agents maybe applied either to the paper or to the fibers prior to their formation into paper. Partially acetylated cellulose paper, however, often exhibits considerable resistance to sizing operations.

One object of our invention is to provide partially acetylated paper, the wet strength and fold values of which are comparable with, or better than, those of a paper prepared from fibers which have not been partially acetylated. Another object of our invention is to provide a paper which is highly resistant to the effects of moisture and which has dimensional stability. A further object of our invention is to provide a paper which is useful for electrical insulation purposes. Other objects of our invention will appear herein.

We have found that paper having highly desirable properties may be prepared from ordinary grades of wood pulp if the fibers of that pulp are initially subjected to a partial acetylation so as to impart an acetyl content of 15-25% thereto and, after forming these fibers into a paper sheet, treated with a water emulsion of a cellulose derivative and a plasticizer for the cellulose derivative. Paper is obtained having good wet strength, fold characteristics and improved Mullen.

The cellulose fiber employed may be any type of chemical wood pulp such as kraft pulp, sulfite pulp, or the like. The pulp employed may be either a bleached pulp (if color is important) or unbleached. Procedures for partially acetylating cellulose fibers are described, for instance, in British Patent No. 367,312, US. applications Ser. Nos. 469,624 and 469,846, both now abandoned, of Richter et al., the article entitled Effect of Acetylation on Water-Binding Properties of Cellulose, in Industrial and Engineering Chemistry, volume 35, pages 12064210, November 1943, and application Ser. No. 786,045, now abandoned, of Herdle and Gandy, filed of even date. After the cellulose fibers have been partially acetylated such as to an acetyl content of 15-25% the fibers are formed into a sheet by a conventional prepared from cellulose fibers such I thus treated paper is then run through hot calender rolls to fuse the cellulose compound-plasticizer mixture and to bond the fibers. To retain opacity titanium dioxide may be incorporated in the emulsion as taught in our application Ser. No. 786,431, filed of even date.

is prepared by agitating in water containing a wetting agent. The ammonium salt of ethyl cellulose phthalate useful for treating partially weight which permits penetration of the emulsion throughout the paper sheet. The following examples illustrate our invention.

Example 1 parts of water and 0.5 part of an ammonium salt of ethyl cellulose phthalate and 50 parts of a solution of half-second viscosity cellulose acetate butyrate in dimethyl phthalate. The sheet was then run through squeeze rolls and the water was evaporated whereupon a sheet containing 16% dimethyl'phthalate and 4% of half-second viscosity cellulose acetate butyrate based on the weight of the paper was obtained. This sheet was supercalendered using 4 nips at 140 F. The difierence in physical properties between paper sheet which had not been treated with the emulsion and paper sheet which had been treated with the emulsion are as follows:

After treatment The L values of tear and folds are lengthwise and the C values are crosswise determinations.

Example 2 A wet strength paper having a base weight of 20 pounds per 1000 sq. ft. made from bleached kraft pulp which had been acetylated to an acetyl content of approximately 20% was passed through an emulsion of the following composition: 12 /2 parts of half-second viscosity cellulose butyrate, 12 /2 parts of dimethyl phthalate, parts of butyl alcohol, 49.5 parts of water containing 0.5 part of the ammonium salt of ethyl cellulose phthalate. The paper was run through squeeze rolls and retained approximately 0.7 part of emulsion per part of paper. The water and solvent were evaporated ofi and the paper was supercalendered using 4 nips at 140 F. The difference in physical properties between the paper before treatment and after treatment are as follows:

Before After treatment treatment Mullen 28 36 Wet strength 6% 10 Expansion. 2. 20 1. 60 M.I.T. Folds:

acetyl, propionyl or butyryl may replace the acetyl fully or in part such as by partially esterifying the fibers with baths in which propionic acid or anhydride or butyric acid or anhydride are used.

We claim:

1. A method for preparing an improved paper of partially acetylated chemical wood pulp fibers having an acetyl content of 15-25%, which comprises impregnating the paper with an aqueous emulsion, the solids content of which essentially consists of one part of a cellulose derivative selected from the group consisting of the lower fatty acid esters of cellulose and ethyl cellulose and l-4 parts of a water-insoluble aliphatic alcohol-organic acid ester plasticizer therefor, the parts all being by weight, drying the paper and subjecting it to heat and pressure to impart a smooth finish thereto.

2. A method of preparing an improved paper of partially acetylated chemical wood pulp fibers having an acetyl content of 15-25%, which comprises impregnating the paper with an aqueous emulsion, the solids content of which essentially consists of one part of a butyric acid ester of cellulose and 1-4 parts of a water-insoluble aliphatic alcohol-organic acid ester plasticizer therefor, the parts all being by weight, drying the paper and subjectiug it to heat and pressure to impart a smooth finish thereto.

3. A method of preparing an improved paper of partially acetylated chemical wood pulp fibers having an acetyl content of 15-25%, which comprises impregnating the paper with an aqueous emulsion, the solids content of which essentially consists of one part of a cellulose derivatives selected from the group consisting of the lower fatty acid esters of cellulose and ethyl cellulose and 1-4 parts of dimethyl phthalate, the parts all being by weight, drying the paper and subjecting it to heat and pressure to impart a smooth finish thereto.

4. A method of improving paper of partially acetylated chemical wood pulp fibers having an acetyl content of 15-25%, which comprises impregnating the paper with an aqueous emulsion, the solids content of which essentially consists of one part of a butyric acid ester of cellulose and 1-4 parts of dimethyl phthalate, the parts all being by weight, drying the paper and subjecting it to heat and pressure to impart a smooth finish thereto.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD FOR PREPARING AN IMPROVED PAPER OF PARTIALLY ACETYLATED CHEMICAL WOOD PULP FIBERS HAVING AN ACETYL CONTENT OF 15-25%, WHICH COMPRISES IMPREGNATING THE PAPER WITH AN AQUEOUS EMULSION, THE SOLIDS CONTENT OF WHICH ESSENTIALLY CONSISTS OF ONE PART OF A CELLULOSE DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF THE LOWER FATTY ACID ESTERS OF CELLULOSE AND ETHYL CELLULOSE AND 1-4 PARTS OF A WATER-INSOLUBLE ALIPHATIC ALCOHOL-OR GANIC ACID ESTER PLASTICIZER THEREOF, THE PARTS ALL BEING BY WEIGHT DRYING THE PAPER AND SUBJECTING IT TO HEAT AND PRESSURE TO IMPART A SMOOTH FINISH THERETO. 